Washington, D.C.—President Donald Trump poses for a portrait in the Oval Office on April 21. In the days before April 29, which marks the 100th day of his administration, Trump posted a tweet complaining that it was unfair to grade him on such a short period in office, even though he vowed on the campaign trail to complete at least 60 of his policy proposals during his first 100 days. Supporters call the appointment of Supreme Court Justice Neil Gorsuch and the dismantling of a swath of Obama-era regulations successes, while the debacle over a health care bill was a notable failure.

NASA scientists announced today that Enceladus, the sixth-largest moon of Saturn, has hydrothermal vents that are actively releasing hydrogen. Because such ecosystems are known to support life, the discovery confirms that Enceladus is a habitable environment.